// Copyright 2006 Google Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.


// Known Issues:
//
// * Patterns only support repeat.
// * Radial gradient are not implemented. The VML version of these look very
//   different from the canvas one.
// * Clipping paths are not implemented.
// * Coordsize. The width and height attribute have higher priority than the
//   width and height style values which isn't correct.
// * Painting mode isn't implemented.
// * Canvas width/height should is using content-box by default. IE in
//   Quirks mode will draw the canvas using border-box. Either change your
//   doctype to HTML5
//   (http://www.whatwg.org/specs/web-apps/current-work/#the-doctype)
//   or use Box Sizing Behavior from WebFX
//   (http://webfx.eae.net/dhtml/boxsizing/boxsizing.html)
// * Non uniform scaling does not correctly scale strokes.
// * Optimize. There is always room for speed improvements.

// AMD by kener.linfeng@gmail.com
// Optimized by https://github.com/pissang
//
// NOTES http://jsperf.com/dom-attr-read-perf/2
// http://jsperf.com/arr-vs-obj-in-ie
define(function (require) {

// Only add this code if we do not already have a canvas implementation
    if (!document.createElement('canvas').getContext) {

        (function () {

            // alias some functions to make (compiled) code shorter
            var m = Math;
            var mr = m.round;
            var ms = m.sin;
            var mc = m.cos;
            var abs = m.abs;
            var sqrt = m.sqrt;

            // this is used for sub pixel precision
            var Z = 10;
            var Z2 = Z / 2;

            var IE_VERSION = +navigator.userAgent.match(/MSIE ([\d.]+)?/)[1];

            var EPSILON = 1e-5;
            var isAroundZero = function (val) {
                return val > -EPSILON && val < EPSILON;
            }

            function isNotAroundZero(val) {
                return val > EPSILON || val < -EPSILON;
            }

            /**
             * This funtion is assigned to the <canvas> elements as element.getContext().
             * @this {HTMLElement}
             * @return {CanvasRenderingContext2D_}
             */
            function getContext() {
                return this.context_ ||
                    (this.context_ = new CanvasRenderingContext2D_(this));
            }

            var slice = Array.prototype.slice;

            /**
             * Binds a function to an object. The returned function will always use the
             * passed in {@code obj} as {@code this}.
             *
             * Example:
             *
             *   g = bind(f, obj, a, b)
             *   g(c, d) // will do f.call(obj, a, b, c, d)
             *
             * @param {Function} f The function to bind the object to
             * @param {Object} obj The object that should act as this when the function
             *     is called
             * @param {*} var_args Rest arguments that will be used as the initial
             *     arguments when the function is called
             * @return {Function} A new function that has bound this
             */
            function bind(f, obj, var_args) {
                var a = slice.call(arguments, 2);
                return function () {
                    return f.apply(obj, a.concat(slice.call(arguments)));
                };
            }

            function encodeHtmlAttribute(s) {
                return String(s).replace(/&/g, '&amp;').replace(/"/g, '&quot;');
            }

            function addNamespace(doc, prefix, urn) {
                if (!doc.namespaces[prefix]) {
                    // NOTES, It will not work proply if add '#default#VML'
                    // When using appendChild to add dom
                    // doc.namespaces.add(prefix, urn, '#default#VML');
                    doc.namespaces.add(prefix, urn);
                }
            }

            function addNamespacesAndStylesheet(doc) {
                addNamespace(doc, 'g_vml_', 'urn:schemas-microsoft-com:vml');
                addNamespace(doc, 'g_o_', 'urn:schemas-microsoft-com:office:office');

                // Setup default CSS.  Only add one style sheet per document
                if (!doc.styleSheets['ex_canvas_']) {
                    var ss = doc.createStyleSheet();
                    ss.owningElement.id = 'ex_canvas_';
                    ss.cssText = 'canvas{display:inline-block;overflow:hidden;' +
                        // default size is 300x150 in Gecko and Opera
                        'text-align:left;width:300px;height:150px} .g_vml_ {behavior:url(#default#VML);}';
                }
            }

            function createVMLElement(tagName) {
                // NOTES Why using createElement needs to add behavior:url(#default#VML) in style
                var dom = document.createElement('<g_vml_:' + tagName + ' class="g_vml_">');
                return dom;

            }

            // Add namespaces and stylesheet at startup.
            addNamespacesAndStylesheet(document);

            var G_vmlCanvasManager_ = {
                init: function (opt_doc) {
                    var doc = opt_doc || document;
                    // Create a dummy element so that IE will allow canvas elements to be
                    // recognized.
                    doc.createElement('canvas');
                    doc.attachEvent('onreadystatechange', bind(this.init_, this, doc));
                },

                init_: function (doc) {
                    // find all canvas elements
                    var els = doc.getElementsByTagName('canvas');
                    for (var i = 0; i < els.length; i++) {
                        this.initElement(els[i]);
                    }
                },

                /**
                 * Public initializes a canvas element so that it can be used as canvas
                 * element from now on. This is called automatically before the page is
                 * loaded but if you are creating elements using createElement you need to
                 * make sure this is called on the element.
                 * @param {HTMLElement} el The canvas element to initialize.
                 * @return {HTMLElement} the element that was created.
                 */
                initElement: function (el) {
                    if (!el.getContext) {
                        el.getContext = getContext;

                        // Add namespaces and stylesheet to document of the element.
                        addNamespacesAndStylesheet(el.ownerDocument);

                        // Remove fallback content. There is no way to hide text nodes so we
                        // just remove all childNodes. We could hide all elements and remove
                        // text nodes but who really cares about the fallback content.
                        el.innerHTML = '';

                        // do not use inline function because that will leak memory
                        el.attachEvent('onpropertychange', onPropertyChange);
                        el.attachEvent('onresize', onResize);

                        var attrs = el.attributes;
                        if (attrs.width && attrs.width.specified) {
                            // TODO: use runtimeStyle and coordsize
                            // el.getContext().setWidth_(attrs.width.nodeValue);
                            el.style.width = attrs.width.nodeValue + 'px';
                        } else {
                            el.width = el.clientWidth;
                        }
                        if (attrs.height && attrs.height.specified) {
                            // TODO: use runtimeStyle and coordsize
                            // el.getContext().setHeight_(attrs.height.nodeValue);
                            el.style.height = attrs.height.nodeValue + 'px';
                        } else {
                            el.height = el.clientHeight;
                        }
                        //el.getContext().setCoordsize_()
                    }
                    return el;
                }
            };

            function onPropertyChange(e) {
                var el = e.srcElement;

                switch (e.propertyName) {
                    case 'width':
                        el.getContext().clearRect();
                        el.style.width = el.attributes.width.nodeValue + 'px';
                        // In IE8 this does not trigger onresize.
                        el.firstChild.style.width = el.clientWidth + 'px';
                        break;
                    case 'height':
                        el.getContext().clearRect();
                        el.style.height = el.attributes.height.nodeValue + 'px';
                        el.firstChild.style.height = el.clientHeight + 'px';
                        break;
                }
            }

            function onResize(e) {
                var el = e.srcElement;
                if (el.firstChild) {
                    el.firstChild.style.width = el.clientWidth + 'px';
                    el.firstChild.style.height = el.clientHeight + 'px';
                }
            }

            G_vmlCanvasManager_.init();

            // precompute "00" to "FF"
            var decToHex = [];
            for (var i = 0; i < 16; i++) {
                for (var j = 0; j < 16; j++) {
                    decToHex[i * 16 + j] = i.toString(16) + j.toString(16);
                }
            }

            function createMatrixIdentity() {
                return [
                    [1, 0, 0],
                    [0, 1, 0],
                    [0, 0, 1]
                ];
            }

            function matrixMultiply(m1, m2) {
                var result = createMatrixIdentity();

                for (var x = 0; x < 3; x++) {
                    for (var y = 0; y < 3; y++) {
                        var sum = 0;

                        for (var z = 0; z < 3; z++) {
                            sum += m1[x][z] * m2[z][y];
                        }

                        result[x][y] = sum;
                    }
                }
                return result;
            }


            function copyState(o1, o2) {
                o2.fillStyle = o1.fillStyle;
                o2.lineCap = o1.lineCap;
                o2.lineJoin = o1.lineJoin;
                o2.lineWidth = o1.lineWidth;
                o2.miterLimit = o1.miterLimit;
                o2.strokeStyle = o1.strokeStyle;
                o2.globalAlpha = o1.globalAlpha;
                o2.font = o1.font;
                o2.textAlign = o1.textAlign;
                o2.textBaseline = o1.textBaseline;
                o2.scaleX_ = o1.scaleX_;
                o2.scaleY_ = o1.scaleY_;
                o2.x_ = o1.x_;
                o2.y_ = o1.y_;
                o2.lineScale_ = o1.lineScale_;
            }

            var colorData = {
                aliceblue: '#F0F8FF',
                antiquewhite: '#FAEBD7',
                aquamarine: '#7FFFD4',
                azure: '#F0FFFF',
                beige: '#F5F5DC',
                bisque: '#FFE4C4',
                black: '#000000',
                blanchedalmond: '#FFEBCD',
                blueviolet: '#8A2BE2',
                brown: '#A52A2A',
                burlywood: '#DEB887',
                cadetblue: '#5F9EA0',
                chartreuse: '#7FFF00',
                chocolate: '#D2691E',
                coral: '#FF7F50',
                cornflowerblue: '#6495ED',
                cornsilk: '#FFF8DC',
                crimson: '#DC143C',
                cyan: '#00FFFF',
                darkblue: '#00008B',
                darkcyan: '#008B8B',
                darkgoldenrod: '#B8860B',
                darkgray: '#A9A9A9',
                darkgreen: '#006400',
                darkgrey: '#A9A9A9',
                darkkhaki: '#BDB76B',
                darkmagenta: '#8B008B',
                darkolivegreen: '#556B2F',
                darkorange: '#FF8C00',
                darkorchid: '#9932CC',
                darkred: '#8B0000',
                darksalmon: '#E9967A',
                darkseagreen: '#8FBC8F',
                darkslateblue: '#483D8B',
                darkslategray: '#2F4F4F',
                darkslategrey: '#2F4F4F',
                darkturquoise: '#00CED1',
                darkviolet: '#9400D3',
                deeppink: '#FF1493',
                deepskyblue: '#00BFFF',
                dimgray: '#696969',
                dimgrey: '#696969',
                dodgerblue: '#1E90FF',
                firebrick: '#B22222',
                floralwhite: '#FFFAF0',
                forestgreen: '#228B22',
                gainsboro: '#DCDCDC',
                ghostwhite: '#F8F8FF',
                gold: '#FFD700',
                goldenrod: '#DAA520',
                grey: '#808080',
                greenyellow: '#ADFF2F',
                honeydew: '#F0FFF0',
                hotpink: '#FF69B4',
                indianred: '#CD5C5C',
                indigo: '#4B0082',
                ivory: '#FFFFF0',
                khaki: '#F0E68C',
                lavender: '#E6E6FA',
                lavenderblush: '#FFF0F5',
                lawngreen: '#7CFC00',
                lemonchiffon: '#FFFACD',
                lightblue: '#ADD8E6',
                lightcoral: '#F08080',
                lightcyan: '#E0FFFF',
                lightgoldenrodyellow: '#FAFAD2',
                lightgreen: '#90EE90',
                lightgrey: '#D3D3D3',
                lightpink: '#FFB6C1',
                lightsalmon: '#FFA07A',
                lightseagreen: '#20B2AA',
                lightskyblue: '#87CEFA',
                lightslategray: '#778899',
                lightslategrey: '#778899',
                lightsteelblue: '#B0C4DE',
                lightyellow: '#FFFFE0',
                limegreen: '#32CD32',
                linen: '#FAF0E6',
                magenta: '#FF00FF',
                mediumaquamarine: '#66CDAA',
                mediumblue: '#0000CD',
                mediumorchid: '#BA55D3',
                mediumpurple: '#9370DB',
                mediumseagreen: '#3CB371',
                mediumslateblue: '#7B68EE',
                mediumspringgreen: '#00FA9A',
                mediumturquoise: '#48D1CC',
                mediumvioletred: '#C71585',
                midnightblue: '#191970',
                mintcream: '#F5FFFA',
                mistyrose: '#FFE4E1',
                moccasin: '#FFE4B5',
                navajowhite: '#FFDEAD',
                oldlace: '#FDF5E6',
                olivedrab: '#6B8E23',
                orange: '#FFA500',
                orangered: '#FF4500',
                orchid: '#DA70D6',
                palegoldenrod: '#EEE8AA',
                palegreen: '#98FB98',
                paleturquoise: '#AFEEEE',
                palevioletred: '#DB7093',
                papayawhip: '#FFEFD5',
                peachpuff: '#FFDAB9',
                peru: '#CD853F',
                pink: '#FFC0CB',
                plum: '#DDA0DD',
                powderblue: '#B0E0E6',
                rosybrown: '#BC8F8F',
                royalblue: '#4169E1',
                saddlebrown: '#8B4513',
                salmon: '#FA8072',
                sandybrown: '#F4A460',
                seagreen: '#2E8B57',
                seashell: '#FFF5EE',
                sienna: '#A0522D',
                skyblue: '#87CEEB',
                slateblue: '#6A5ACD',
                slategray: '#708090',
                slategrey: '#708090',
                snow: '#FFFAFA',
                springgreen: '#00FF7F',
                steelblue: '#4682B4',
                tan: '#D2B48C',
                thistle: '#D8BFD8',
                tomato: '#FF6347',
                turquoise: '#40E0D0',
                violet: '#EE82EE',
                wheat: '#F5DEB3',
                whitesmoke: '#F5F5F5',
                yellowgreen: '#9ACD32'
            };

            function getRgbHslContent(styleString) {
                var start = styleString.indexOf('(', 3);
                var end = styleString.indexOf(')', start + 1);
                var parts = styleString.substring(start + 1, end).split(',');
                // add alpha if needed
                if (parts.length != 4 || styleString.charAt(3) != 'a') {
                    parts[3] = 1;
                }
                return parts;
            }

            function percent(s) {
                return parseFloat(s) / 100;
            }

            function clamp(v, min, max) {
                return Math.min(max, Math.max(min, v));
            }

            function hslToRgb(parts) {
                var r, g, b, h, s, l;
                h = parseFloat(parts[0]) / 360 % 360;
                if (h < 0)
                    h++;
                s = clamp(percent(parts[1]), 0, 1);
                l = clamp(percent(parts[2]), 0, 1);
                if (s == 0) {
                    r = g = b = l; // achromatic
                } else {
                    var q = l < 0.5 ? l * (1 + s) : l + s - l * s;
                    var p = 2 * l - q;
                    r = hueToRgb(p, q, h + 1 / 3);
                    g = hueToRgb(p, q, h);
                    b = hueToRgb(p, q, h - 1 / 3);
                }

                return '#' + decToHex[Math.floor(r * 255)] +
                    decToHex[Math.floor(g * 255)] +
                    decToHex[Math.floor(b * 255)];
            }

            function hueToRgb(m1, m2, h) {
                if (h < 0)
                    h++;
                if (h > 1)
                    h--;

                if (6 * h < 1)
                    return m1 + (m2 - m1) * 6 * h;
                else if (2 * h < 1)
                    return m2;
                else if (3 * h < 2)
                    return m1 + (m2 - m1) * (2 / 3 - h) * 6;
                else
                    return m1;
            }

            var processStyleCache = {};

            function processStyle(styleString) {
                if (styleString in processStyleCache) {
                    return processStyleCache[styleString];
                }

                var str, alpha = 1;

                styleString = String(styleString);
                if (styleString.charAt(0) == '#') {
                    str = styleString;
                } else if (/^rgb/.test(styleString)) {
                    var parts = getRgbHslContent(styleString);
                    var str = '#', n;
                    for (var i = 0; i < 3; i++) {
                        if (parts[i].indexOf('%') != -1) {
                            n = Math.floor(percent(parts[i]) * 255);
                        } else {
                            n = +parts[i];
                        }
                        str += decToHex[clamp(n, 0, 255)];
                    }
                    alpha = +parts[3];
                } else if (/^hsl/.test(styleString)) {
                    var parts = getRgbHslContent(styleString);
                    str = hslToRgb(parts);
                    alpha = parts[3];
                } else {
                    str = colorData[styleString] || styleString;
                }
                return processStyleCache[styleString] = {color: str, alpha: alpha};
            }

            var DEFAULT_STYLE = {
                style: 'normal',
                variant: 'normal',
                weight: 'normal',
                size: 12,           //10
                family: '微软雅黑'     //'sans-serif'
            };

            // Internal text style cache
            var fontStyleCache = {};

            function processFontStyle(styleString) {
                if (fontStyleCache[styleString]) {
                    return fontStyleCache[styleString];
                }

                var el = document.createElement('div');
                var style = el.style;
                var fontFamily;
                try {
                    style.font = styleString;
                    fontFamily = style.fontFamily.split(',')[0];
                } catch (ex) {
                    // Ignore failures to set to invalid font.
                }

                return fontStyleCache[styleString] = {
                    style: style.fontStyle || DEFAULT_STYLE.style,
                    variant: style.fontVariant || DEFAULT_STYLE.variant,
                    weight: style.fontWeight || DEFAULT_STYLE.weight,
                    size: style.fontSize || DEFAULT_STYLE.size,
                    family: fontFamily || DEFAULT_STYLE.family
                };
            }

            function getComputedStyle(style, element) {
                var computedStyle = {};

                for (var p in style) {
                    computedStyle[p] = style[p];
                }

                // Compute the size
                var canvasFontSize = parseFloat(element.currentStyle.fontSize),
                    fontSize = parseFloat(style.size);

                if (typeof style.size == 'number') {
                    computedStyle.size = style.size;
                } else if (style.size.indexOf('px') != -1) {
                    computedStyle.size = fontSize;
                } else if (style.size.indexOf('em') != -1) {
                    computedStyle.size = canvasFontSize * fontSize;
                } else if (style.size.indexOf('%') != -1) {
                    computedStyle.size = (canvasFontSize / 100) * fontSize;
                } else if (style.size.indexOf('pt') != -1) {
                    computedStyle.size = fontSize / .75;
                } else {
                    computedStyle.size = canvasFontSize;
                }

                // Different scaling between normal text and VML text. This was found using
                // trial and error to get the same size as non VML text.
                //computedStyle.size *= 0.981;

                return computedStyle;
            }

            function buildStyle(style) {
                return style.style + ' ' + style.variant + ' ' + style.weight + ' ' +
                    style.size + "px '" + style.family + "'";
            }

            var lineCapMap = {
                'butt': 'flat',
                'round': 'round'
            };

            function processLineCap(lineCap) {
                return lineCapMap[lineCap] || 'square';
            }

            function createShapeAttr() {
                return {
                    filled: false,
                    stroked: false,

                    path: '',
                    fillStyle: null,
                    strokeStyle: null,

                    globalAlpha: 1,
                    lineCap: 'butt',
                    lineJoin: 'miter',
                    lineWidth: 1,
                    miterlimit: Z * 1,

                    x: 0,
                    y: 0
                };
            }

            function copyShapeAttr(o1, o2) {
                o1.path = o2.path;

                o1.fillStyle = o2.fillStyle;

                o1.globalAlpha = o2.globalAlpha;

                // PENDING When shape changed from not stroked to stroked
                if (o2.stroked) {
                    o1.strokeStyle = o2.strokeStyle;
                    o1.lineCap = o2.lineCap;
                    o1.lineJoin = o2.lineJoin;
                    o1.lineWidth = o2.lineWidth;
                    o1.miterlimit = o2.miterlimit;
                }

                o1.x = o2.x;
                o1.y = o2.y;

                o1.filled = o2.filled;
                o1.stroked = o2.stroked;
            }

            function createTextAttr() {
                var attr = createShapeAttr();
                attr.text = '';
                attr.font = '12px 微软雅黑';
                attr.textAlign = 'left';
                attr.textBaseline = 'alphabetic';
                attr.offX = 0;
                attr.offY = 0;
                attr.maxWidth = 0;

                return attr;
            }

            function copyTextAttr(o1, o2) {
                copyShapeAttr(o1, o2);

                o1.text = o2.text;
                o1.font = o2.font;
                o1.textAlign = o2.textAlign;
                o1.textBaseline = o2.textBaseline;
                o1.offX = o2.offX;
                o1.offY = o2.offY;
                o1.maxWidth = o2.maxWidth;
            }

            function createImageAttr() {
                return {
                    image: '',
                    // position after tranformed
                    x: 0,
                    y: 0,
                    padding: '',
                    skewM: '',
                    cropped: false,
                    width: 0,
                    height: 0,
                    globalAlpha: 1
                };
            }

            function copyImageAttr(o1, o2) {
                o1.image = o2.image;
                o1.x = o2.x;
                o1.y = o2.y;
                o1.width = o2.width;
                o1.height = o2.height;
                o1.globalAlpha = o2.globalAlpha;

                if (o2.skewed) {
                    o1.skewM = o2.skewM;
                    o1.padding = o2.padding;
                }

                if (o2.cropped) {
                    o1.cropWidth = o2.cropWidth;
                    o1.cropHeight = o2.cropHeight;
                    o1.cropFilter = o2.cropFilter;
                }

                o1.cropped = o2.cropped;
                o1.skewed = o2.skewed;
            }

            /**
             * Virtual shape dom is created by stroke and fill operation.
             * It will be cached in Context2D object. And created only if needed when redrawing
             * @author https://github.com/pissang/
             */
            function ShapeVirtualDom_() {
                // this.rootEl_ = null;
                // this.strokeEl_ = null;
                // this.fillEl_ = null;

                this.attr_ = createShapeAttr();

                this.attrPrev_ = {};
            }

            ShapeVirtualDom_.prototype.attachTo = function (el) {
                if (!this.attached_) {
                    var p = this.rootEl_.parentNode;
                    if (p !== el) {
                        el.appendChild(this.rootEl_);
                    }
                }
                this.attached_ = true;
            }

            ShapeVirtualDom_.prototype.detach = function () {
                if (this.attached_) {
                    var p = this.rootEl_.parentNode;
                    if (p) {
                        p.removeChild(this.rootEl_);
                    }
                }
                this.attached_ = false;
            }

            ShapeVirtualDom_.prototype.getElement = function (path) {
                if (!this.rootEl_) {
                    this.createShapeEl_(path);
                }
                var attr_ = this.attr_;
                attr_.path = path;
                attr_.filled = false;
                attr_.stroked = false;

                return this.rootEl_;
            };

            ShapeVirtualDom_.prototype.createShapeEl_ = function (path) {

                var W = 10;
                var H = 10;

                var rootEl_ = createVMLElement('shape');
                rootEl_.style.cssText = ['position:absolute;width:', W, 'px;height:', H, 'px'].join('');
                rootEl_.coordorigin = '0 0';
                rootEl_.coordsize = Z * W + ' ' + Z * H;

                rootEl_.filled = 'false';
                rootEl_.stroked = 'false';

                this.rootEl_ = rootEl_;
            };

            ShapeVirtualDom_.prototype.isFilled = function () {
                return this.attr_.filled;
            };

            ShapeVirtualDom_.prototype.isStroked = function () {
                return this.attr_.stroked;
            };

            ShapeVirtualDom_.prototype.fill = function (ctx, min, max) {
                var attr_ = this.attr_;

                attr_.filled = true;
                attr_.fillStyle = ctx.fillStyle;
                attr_.globalAlpha = ctx.globalAlpha;

                attr_.x = ctx.x_;
                attr_.y = ctx.y_;

                if (ctx.fillStyle instanceof CanvasGradient_) {
                    attr_.m_ = ctx.m_;
                    attr_.scaleX = ctx.scaleX_;
                    attr_.scaleY = ctx.scaleY_;
                    attr_.min = min;
                    attr_.max = max;
                } else if (ctx.fillStyle instanceof CanvasPattern_) {
                    attr_.scaleX = ctx.scaleX_;
                    attr_.scaleY = ctx.scaleY_;
                    attr_.min = min;
                    attr_.max = max;
                }
            };

            ShapeVirtualDom_.prototype.stroke = function (ctx) {
                var attr_ = this.attr_;

                attr_.stroked = true;
                attr_.globalAlpha = ctx.globalAlpha;
                attr_.lineCap = ctx.lineCap;
                attr_.lineJoin = ctx.lineJoin;
                attr_.lineWidth = ctx.lineWidth * ctx.lineScale_;
                attr_.miterlimit = ctx.miterlimit;
                attr_.strokeStyle = ctx.strokeStyle;

                attr_.x = ctx.x_;
                attr_.y = ctx.y_;
            }

            ShapeVirtualDom_.prototype.doFill_ = function () {
                var attr_ = this.attr_;
                var attrPrev_ = this.attrPrev_;
                if (attr_.filled !== attrPrev_.filled) {
                    var rootEl_ = this.rootEl_;
                    if (attr_.filled) {
                        rootEl_.filled = 'true';
                        if (!this.fillEl_) {
                            this.fillEl_ = createVMLElement('fill');
                            // PENDING
                            // Set default attribute ?
                        }
                        rootEl_.appendChild(this.fillEl_);
                    } else {
                        rootEl_.filled = 'false';
                        if (this.fillEl_) {
                            rootEl_.removeChild(this.fillEl_);
                        }
                    }
                }
                if (!attr_.filled) {
                    return;
                }

                var fillEl_ = this.fillEl_;

                var fillStyle = attr_.fillStyle;

                if (
                    fillStyle !== attrPrev_.fillStyle ||
                    attr_.globalAlpha !== attrPrev_.globalAlpha
                ) {
                    // TODO Canvas gradient and pattern still not be optimized
                    // There problem when canvas gradient add color stop dynamically
                    //
                    // Text fill doesn't support Gradient or Pattern
                    if ((fillStyle instanceof CanvasGradient_) && attr_.min) {
                        // TODO: Gradients transformed with the transformation matrix.
                        var angle = 0;
                        var focus = {x: 0, y: 0};

                        // additional offset
                        var shift = 0;
                        // scale factor for offset
                        var expansion = 1;

                        var scaleX = attr_.scaleX_;
                        var scaleY = attr_.scaleY_;
                        var min = attr_.min;
                        var max = attr_.max;
                        var width = max.x - min.x;
                        var height = max.y - min.y;

                        if (fillStyle.type_ == 'gradient') {
                            var x0 = fillStyle.x0_ / scaleX;
                            var y0 = fillStyle.y0_ / scaleY;
                            var x1 = fillStyle.x1_ / scaleX;
                            var y1 = fillStyle.y1_ / scaleY;
                            var p0 = getCoords(ctx, x0, y0);
                            var p1 = getCoords(ctx, x1, y1);
                            var dx = p1.x - p0.x;
                            var dy = p1.y - p0.y;
                            angle = Math.atan2(dx, dy) * 180 / Math.PI;

                            // The angle should be a non-negative number.
                            if (angle < 0) {
                                angle += 360;
                            }

                            // Very small angles produce an unexpected result because they are
                            // converted to a scientific notation string.
                            if (angle < 1e-6) {
                                angle = 0;
                            }
                        } else {
                            var p0 = getCoords(ctx, fillStyle.x0_, fillStyle.y0_);
                            focus = {
                                x: (p0.x - min.x) / width,
                                y: (p0.y - min.y) / height
                            };

                            width /= scaleX * Z;
                            height /= scaleY * Z;
                            var dimension = m.max(width, height);
                            shift = 2 * fillStyle.r0_ / dimension;
                            expansion = 2 * fillStyle.r1_ / dimension - shift;
                        }

                        // We need to sort the color stops in ascending order by offset,
                        // otherwise IE won't interpret it correctly.
                        var stops = fillStyle.colors_;
                        stops.sort(function (cs1, cs2) {
                            return cs1.offset - cs2.offset;
                        });

                        var length = stops.length;
                        var color1 = stops[0].color;
                        var color2 = stops[length - 1].color;
                        var opacity1 = stops[0].alpha * attr_.globalAlpha;
                        var opacity2 = stops[length - 1].alpha * attr_.globalAlpha;

                        var colors = [];
                        for (var i = 0; i < length; i++) {
                            var stop = stops[i];
                            colors.push(stop.offset * expansion + shift + ' ' + stop.color);
                        }

                        fillEl_.type = fillStyle.type_;
                        fillEl_.method = 'none';
                        fillEl_.focus = '100%';
                        fillEl_.color = color1;
                        fillEl_.color2 = color2;
                        fillEl_.colors = colors.join(',');
                        fillEl_.opacity = opacity2;
                        fillEl_.setAttribute('g_o_:opacity2', opacity1);
                        fillEl_.angle = angle;
                        fillEl_.focusposition = focus.x + ',' + focus.y;
                    } else if ((fillStyle instanceof CanvasPattern_) && attr_.min) {
                        if (width && height) {
                            var deltaLeft = -attr_.min.x;
                            var deltaTop = -attr_.min.y;
                            fillEl_.position = deltaLeft / width * scaleX * scaleX + ',' +
                                deltaTop / height * scaleY * scaleY;
                            fillEl_.type = 'tile';
                            fillEl_.src = fillStyle.src_;
                        }
                    } else {
                        var a = processStyle(fillStyle);
                        var color = a.color;
                        var opacity = a.alpha * attr_.globalAlpha;
                        fillEl_.color = color;
                        if (opacity < 1) {
                            fillEl_.opacity = opacity;
                        }
                    }
                }
            };

            ShapeVirtualDom_.prototype.doStroke_ = function () {
                var attr_ = this.attr_;
                var attrPrev_ = this.attrPrev_;
                if (attr_.stroked !== attrPrev_.stroked) {
                    var rootEl_ = this.rootEl_;
                    if (attr_.stroked) {
                        if (!this.strokeEl_) {
                            this.strokeEl_ = createVMLElement('stroke');
                            // PENDING
                            // Set default attribute ?
                        }
                        rootEl_.stroked = 'true';
                        rootEl_.appendChild(this.strokeEl_);
                    } else {
                        rootEl_.stroked = 'false';
                        if (this.strokeEl_) {
                            rootEl_.removeChild(this.strokeEl_);
                        }
                    }
                }

                if (!attr_.stroked) {
                    return;
                }

                if (
                    attr_.strokeStyle !== attrPrev_.strokeStyle ||
                    attr_.globalAlpha !== attrPrev_.globalAlpha ||
                    attr_.lineWidth !== attrPrev_.lineWidth
                ) {
                    var a = processStyle(attr_.strokeStyle);
                    var opacity = a.alpha * attr_.globalAlpha;
                    var lineWidth = attr_.lineWidth;
                    // VML cannot correctly render a line if the width is less than 1px.
                    // In that case, we dilute the color to make the line look thinner.
                    if (lineWidth < 1) {
                        opacity *= lineWidth;
                    }
                    if (opacity < 1) {
                        this.strokeEl_.opacity = opacity;
                    }
                    this.strokeEl_.color = a.color;
                }
                if (attr_.lineJoin !== attrPrev_.lineJoin) {
                    this.strokeEl_.joinstyle = attr_.lineJoin;
                }
                if (attr_.miterLimit !== attrPrev_.miterLimit) {
                    this.strokeEl_.miterlimit = attr_.miterLimit;
                }
                if (attr_.lineCap !== attrPrev_.lineCap) {
                    this.strokeEl_.endcap = processLineCap(attr_.lineCap);
                }
                if (lineWidth !== attrPrev_.lineWidth) {
                    this.strokeEl_.weight = lineWidth + 'px';
                }
            };

            ShapeVirtualDom_.prototype.flush = function (ctx) {
                var attr_ = this.attr_;
                var attrPrev_ = this.attrPrev_;
                if (attr_.x !== attrPrev_.x) {
                    this.rootEl_.style.left = attr_.x + 'px';
                }
                if (attr_.y !== attrPrev_.y) {
                    this.rootEl_.style.top = attr_.y + 'px';
                }
                if (attr_.path !== attrPrev_.path) {
                    this.rootEl_.path = attr_.path;
                }
                this.doFill_();
                this.doStroke_();

                copyShapeAttr(attrPrev_, attr_);
            }

            /**
             * Virtual text dom is created by fillText and strokeText operation.
             * It will be cached in Context2D object. And created only if needed when redrawing
             * @author https://github.com/pissang/
             */
            function TextVirtualDom_() {
                // this.rootEl_ = null;
                // this.skewEl_ = null;
                // this.textPathEl_ = null;
                // this.simpleRootEl_ = null;

                this.attr_ = createTextAttr();
                this.attrPrev_ = {};
            }

            TextVirtualDom_.prototype.getElement = function (ctx, text, x, y, maxWidth, stroke) {
                if (!this.rootEl_) {
                    this.createEl_();
                }
                var m_ = ctx.m_;

                var attr_ = this.attr_;
                attr_.text = text;

                attr_.sx = x;
                attr_.sy = y;
                attr_.maxWidth = maxWidth;
                attr_.textAlign = ctx.textAlign;
                attr_.textBaseline = ctx.textBaseline;

                attr_.stroked = !!stroke;
                attr_.filled = !stroke;

                var fontStyle = getComputedStyle(processFontStyle(ctx.font),
                    ctx.element_);
                var fontStyleString = buildStyle(fontStyle);

                attr_.font = fontStyleString;

                var offset = {x: 0, y: 0};
                // 1.75 is an arbitrary number, as there is no info about the text baseline
                switch (ctx.textBaseline) {
                    case 'hanging':
                    case 'top':
                        offset.y = fontStyle.size / 1.75;
                        break;
                    case 'middle':
                        break;
                    default:
                    case null:
                    case 'alphabetic':
                    case 'ideographic':
                    case 'bottom':
                        offset.y = -fontStyle.size / 2.25;
                        break;
                }

                var d = getCoords(ctx, x + offset.x, y + offset.y);
                attr_.offX = d.x;
                attr_.offY = d.y;
                // attr_.skewed = isNotAroundZero(m_[0] - 1) || isNotAroundZero(m_[1]) ||
                // isNotAroundZero(m_[3] - 1) || isNotAroundZero(m_[2])
                attr_.skewM = m_[0][0].toFixed(3) + ',' + m_[1][0].toFixed(3) + ',' +
                    m_[0][1].toFixed(3) + ',' + m_[1][1].toFixed(3);

                if (stroke) {
                    attr_.globalAlpha = ctx.globalAlpha;
                    attr_.lineCap = ctx.lineCap;
                    attr_.lineJoin = ctx.lineJoin;
                    attr_.lineWidth = ctx.lineWidth * ctx.lineScale_;
                    attr_.miterlimit = ctx.miterlimit;
                    attr_.strokeStyle = ctx.strokeStyle;
                } else {
                    attr_.fillStyle = ctx.fillStyle;
                    attr_.globalAlpha = ctx.globalAlpha;
                }
                // TODO It is strange that flush after the rootEl has been appended to document
                // SkewOffset like '10, 10'(which one item is not zero) will cause the shape disappeared.
                this.flush(ctx);

                return this.rootEl_;
            };

            TextVirtualDom_.prototype.createEl_ = function () {
                var W = 10;
                var H = 10;
                this.rootEl_ = createVMLElement('line');
                var rootEl_ = this.rootEl_;
                rootEl_.coordsize = Z * W + ' ' + Z * H;
                rootEl_.coordorigin = '0 0';
                rootEl_.style.cssText = 'position:absolute;width:1px;height:1px';
                rootEl_.stroked = 'false';
                rootEl_.filled = 'false';
            };

            TextVirtualDom_.prototype.flush = function (ctx) {
                var m_ = ctx.m_;
                var delta = 1000;
                var left = 0;
                var right = delta;
                var attr_ = this.attr_;
                var attrPrev_ = this.attrPrev_;
                var rootEl_ = this.rootEl_;

                if (!this.skewEl_) {
                    this.skewEl_ = createVMLElement('skew');
                    this.skewEl_.on = 't';
                    this.textPathEl_ = createVMLElement('textpath');
                    this.pathEl_ = createVMLElement('path');
                    this.pathEl_.textpathok = 'true';
                    this.textPathEl_.on = 'true';

                    rootEl_.appendChild(this.skewEl_);
                    rootEl_.appendChild(this.pathEl_);
                    rootEl_.appendChild(this.textPathEl_);
                }

                var fontStyle = getComputedStyle(processFontStyle(this.attr_.font),
                    ctx.element_);
                if (
                    attr_.font !== attrPrev_.font ||
                    attr_.text !== attrPrev_.text
                ) {
                    this.textPathEl_.string = encodeHtmlAttribute(attr_.text);
                    this.textPathEl_.style.font = encodeHtmlAttribute(attr_.font);
                }

                if (attr_.textAlign !== attrPrev_.textAlign) {
                    var elementStyle = ctx.element_.currentStyle;
                    var textAlign = attr_.textAlign.toLowerCase();
                    switch (textAlign) {
                        case 'left':
                        case 'center':
                        case 'right':
                            break;
                        case 'end':
                            textAlign = elementStyle.direction == 'ltr' ? 'right' : 'left';
                            break;
                        case 'start':
                            textAlign = elementStyle.direction == 'rtl' ? 'right' : 'left';
                            break;
                        default:
                            textAlign = 'left';
                    }
                    switch (textAlign) {
                        case 'right':
                            left = delta;
                            right = 0.05;
                            break;
                        case 'center':
                            left = right = delta / 2;
                            break;
                    }
                    rootEl_.from = -left + ' 0';
                    rootEl_.to = right + ' 0.05';
                    this.skewEl_.origin = left + ' 0';
                    this.textPathEl_.style['v-text-align'] = textAlign;
                }

                // if (attr_.skewed || stroke) {
                if (attr_.skewM !== attrPrev_.skewM) {
                    this.skewEl_.matrix = attr_.skewM + ',0,0';
                }

                if (attr_.offX !== attrPrev_.offX ||
                    attr_.offY !== attrPrev_.offY
                ) {
                    var skewOffset = mr(attr_.offX / Z) + ',' + mr(attr_.offY / Z);
                    this.skewEl_.offset = skewOffset;
                }

                if (attr_.stroked) {
                    this.doStroke_();
                } else {
                    this.doFill_();
                }

                copyTextAttr(attrPrev_, attr_);

                // } else {
                //   if (!this.simpleRootEl_) {
                //     this.simpleRootEl_ = document.createElement('div');
                //     this.simpleRootEl_.style.position = 'absolute';
                //   }
                //   this.simpleRootEl_.style.font = encodeHtmlAttribute(fontStyleString);

                //   var a = processStyle(ctx.fillStyle);
                //   var color = a.color;
                //   var opacity = a.alpha * ctx.globalAlpha;
                //   this.simpleRootEl_.style.color = color;
                //   if (opacity < 1) {
                //     this.simpleRootEl_.style.filter = 'alpha(opacity=' + mr(opacity * 100) +')';
                //   }

                //   this.simpleRootEl_.innerHTML = text;

                //   switch (ctx.textBaseline) {
                //     case 'hanging':
                //     case 'top':
                //       this.simpleRootEl_.style.top = m_[2][1] + y + 'px';
                //       break;
                //     case 'middle':
                //       // TODO
                //       this.simpleRootEl_.style.top = m_[2][1] + y - fontStyle.size / 2.25 + 'px';
                //       break;
                //     default:
                //     case null:
                //     case 'alphabetic':
                //     case 'ideographic':
                //     case 'bottom':
                //     //
                //       this.simpleRootEl_.style.bottom = ctx.element_.clientHeight - m_[2][1] - y + 'px';
                //       break;
                //   }

                //   switch(textAlign) {
                //     case 'right':
                //       this.simpleRootEl_.style.right = ctx.element_.clientWidth - m_[2][0] - x + 'px';
                //       break;
                //     case 'center':
                //       // TODO
                //       this.simpleRootEl_.style.left = m_[2][0] + x - fontStyle.size / 4.5 * text.length + 'px';
                //       break;
                //     case 'left':
                //       this.simpleRootEl_.style.left = m_[2][0] + x + 'px';
                //       break;
                //   }
                //   return this.simpleRootEl_;
                // }
            }

            TextVirtualDom_.prototype.doFill_ = ShapeVirtualDom_.prototype.doFill_;
            TextVirtualDom_.prototype.doStroke_ = ShapeVirtualDom_.prototype.doStroke_;
            TextVirtualDom_.prototype.attachTo = ShapeVirtualDom_.prototype.attachTo;
            TextVirtualDom_.prototype.detach = ShapeVirtualDom_.prototype.detach;

            /**
             * Virtual image dom is created by drawImage operation.
             * It will be cached in Context2D object. And created only if needed when redrawing
             * @author https://github.com/pissang/
             *
             * TODO Image cropping testing
             */
            function ImageVirtualDom_() {
                // this.rootEl_ = null;
                // this.cropEl_ = null;
                // this.imageEl_ = null;
                // this.groupEl_ = null;

                this.attr_ = createImageAttr();

                this.attrPrev_ = {};
            };

            ImageVirtualDom_.prototype.getElement = function (ctx, image, var_args) {
                var dx, dy, dw, dh, sx, sy, sw, sh;

                // to find the original width we overide the width and height
                var oldRuntimeWidth = image.runtimeStyle.width;
                var oldRuntimeHeight = image.runtimeStyle.height;
                var m_ = ctx.m_;
                image.runtimeStyle.width = 'auto';
                image.runtimeStyle.height = 'auto';

                // get the original size
                var w = image.width;
                var h = image.height;

                // and remove overides
                image.runtimeStyle.width = oldRuntimeWidth;
                image.runtimeStyle.height = oldRuntimeHeight;

                var args = Array.prototype.slice.call(arguments, 1);
                var attr_ = this.attr_;
                attr_.globalAlpha = ctx.globalAlpha;

                var scaleX = ctx.scaleX_;
                var scaleY = ctx.scaleY_;
                if (args.length == 3) {
                    dx = args[1];
                    dy = args[2];
                    sx = sy = 0;
                    sw = dw = w;
                    sh = dh = h;
                } else if (args.length == 5) {
                    dx = args[1];
                    dy = args[2];
                    dw = args[3];
                    dh = args[4];
                    sx = sy = 0;
                    sw = w;
                    sh = h;
                } else if (args.length == 9) {
                    sx = args[1];
                    sy = args[2];
                    sw = args[3];
                    sh = args[4];
                    dx = args[5];
                    dy = args[6];
                    dw = args[7];
                    dh = args[8];
                } else {
                    throw Error('Invalid number of arguments');
                }

                // Have rotation
                attr_.skewed = m_[0][1] || m_[1][0];

                if (attr_.skewed) {
                    var d = getCoords(ctx, dx, dy);
                    attr_.x = d.x;
                    attr_.y = d.y;
                    var filter = [];
                    filter.push('M11=', m_[0][0] / scaleX, ',',
                        'M12=', m_[1][0] / scaleY, ',',
                        'M21=', m_[0][1] / scaleX, ',',
                        'M22=', m_[1][1] / scaleY, ',',
                        'Dx=', d.x, ',',
                        'Dy=', d.y, '');
                    attr_.skewM = filter.join('');

                    // Bounding box calculation (need to minimize displayed area so that
                    // filters don't waste time on unused pixels.
                    var max = d;
                    var c2 = getCoords(ctx, dx + dw, dy);
                    var c3 = getCoords(ctx, dx, dy + dh);
                    var c4 = getCoords(ctx, dx + dw, dy + dh);

                    max.x = m.max(max.x, c2.x, c3.x, c4.x);
                    max.y = m.max(max.y, c2.y, c3.y, c4.y);

                    attr_.padding = [0, Math.max(mr(max.x / Z), 0) + 'px', Math.max(mr(max.y / Z), 0) + 'px', 0].join(' ');
                } else {
                    attr_.x = dx * scaleX + ctx.x_;
                    attr_.y = dy * scaleY + ctx.y_;
                }

                attr_.cropped = sx || sy;
                if (attr_.cropped) {
                    attr_.cropWidth = Math.ceil((dw + sx * dw / sw) * scaleX);
                    attr_.cropHeight = Math.ceil((dh + sy * dh / sh) * scaleY);
                    attr_.cropFilter = 'progid:DxImageTransform.Microsoft.Matrix(Dx='
                        + -dw / sw * scaleX * sx + ',Dy=' + -dh / sh * scaleY * sy + ')';
                }

                attr_.width = scaleX * dw / sw * w;
                attr_.height = scaleY * dh / sh * h;

                attr_.image = image.src;

                if (!this.imageEl_) {
                    // NOTES
                    // Matrix of rootDom will not work if imageDom.style.position = 'absolute'
                    this.imageEl_ = document.createElement('img');
                }

                if (!(attr_.skewed || attr_.cropped)) {
                    this.rootEl_ = this.imageEl_;
                } else if (attr_.skewed) {
                    if (!this.groupEl_) {
                        this.createGroupEl_();
                    }
                    this.rootEl_ = this.groupEl_;
                } else {
                    if (!this.cropEl_) {
                        this.cropEl_ = document.createElement('div');
                        this.cropEl_.style.cssText = 'position:absolute; overflow:hidden;';
                    }
                    this.rootEl_ = this.cropEl_;
                }

                this.flush(ctx);
                return this.rootEl_;
            };

            ImageVirtualDom_.prototype.createGroupEl_ = function () {
                var W = 10;
                var H = 10;

                // For some reason that I've now forgotten, using divs didn't work
                this.groupEl_ = createVMLElement('group');
                this.groupEl_.coordsize = Z * W + ' ' + Z * H;
                this.groupEl_.coordorigin = '0 0';

                this.groupEl_.style.cssText = ['position:absolute;width:', W, 'px;height:', H, 'px'].join('');
            }

            ImageVirtualDom_.prototype.flush = function (ctx) {
                var attr_ = this.attr_;
                var attrPrev_ = this.attrPrev_;
                var w2 = attr_.sw / 2;
                var h2 = attr_.sh / 2;

                var imageEl_ = this.imageEl_;

                // If filters are necessary (rotation exists), create them
                // filters are bog-slow, so only create them if abbsolutely necessary
                // The following check doesn't account for skews (which don't exist
                // in the canvas spec (yet) anyway.
                if (!attr_.skewed && !attr_.cropped) {
                    if (attr_.x !== attrPrev_.x) {
                        imageEl_.style.left = attr_.x + 'px';
                    }
                    if (attr_.y !== attrPrev_.y) {
                        imageEl_.style.top = attr_.y + 'px';
                    }
                    if (!attrPrev_.skewed) {
                        imageEl_.style.position = 'absolute';
                    } else {
                        imageEl_.style.position = 'static';
                    }
                } else if (attr_.skewed) {
                    var groupEl_ = this.groupEl_;
                    if (attr_.padding !== attrPrev_.padding) {
                        groupEl_.style.padding = attr_.padding;
                    }

                    if (attr_.skewM !== attrPrev_.skewM) {
                        groupEl_.style.filter = 'progid:DXImageTransform.Microsoft.Matrix('
                            + attr_.skewM + ", SizingMethod='clip')";
                    }

                    if (attr_.cropped) {
                        if (!attrPrev_.cropped) {
                            groupEl_.appendChild(this.cropEl_);
                            this.cropEl_.appendChild(imageEl_);
                        }
                    } else {
                        if (!attrPrev_.skewed) {
                            groupEl_.appendChild(imageEl_);
                        }
                    }
                } else if (attr_.cropped) {
                    if (!attrPrev_.cropped) {
                        this.cropEl_.appendChild(imageEl_);
                    }
                }

                // Draw a special cropping div if needed
                if (attr_.cropped) {
                    var groupEl_ = this.groupEl_;
                    if (attr_.cropWidth !== attrPrev_.cropWidth) {
                        this.cropEl_.style.width = attr_.cropWidth + 'px';
                    }
                    if (attr_.cropHeight !== attrPrev_.cropHeight) {
                        this.cropEl_.style.height = attr_.cropHeight + 'px';
                    }
                    if (attr_.filter !== attrPrev_.filter) {
                        this.cropEl_.style.filter = attr_.filter;
                    }
                }

                if (attr_.width !== attrPrev_.width) {
                    imageEl_.style.width = attr_.width + 'px';
                }
                if (attr_.height !== attrPrev_.height) {
                    imageEl_.style.height = attr_.height + 'px';
                }

                if (attr_.image !== attrPrev_.image) {
                    imageEl_.src = attr_.image;
                }
                if (attr_.globalAlpha !== attrPrev_.globalAlpha) {
                    if (imageEl_.style.globalAlpha < 1) {
                        imageEl_.style.filter = 'alpha(opacity=' + mr(attr_.globalAlpha * 100) + ')';
                    } else {
                        imageEl_.style.filter = '';
                    }
                }

                copyImageAttr(this.attrPrev_, this.attr_);
            }

            ImageVirtualDom_.prototype.attachTo = ShapeVirtualDom_.prototype.attachTo;
            ImageVirtualDom_.prototype.detach = ShapeVirtualDom_.prototype.detach;

            /**
             * This class implements CanvasRenderingContext2D interface as described by
             * the WHATWG.
             * @param {HTMLElement} canvasElement The element that the 2D context should
             * be associated with
             */
            function CanvasRenderingContext2D_(canvasElement) {
                this.m_ = createMatrixIdentity();

                this.mStack_ = [];
                this.aStack_ = [];
                this.currentPath_ = [];

                // NOTES
                // http://louisremi.com/2009/03/30/changes-in-vml-for-ie8-or-what-feature-can-the-ie-dev-team-break-for-you-today/
                // It is no longer possible to create a VML element outside of the DOM
                // this.fragment_ = document.createDocumentFragment();

                // Keep current drawed dom. So we can merge fill and stroke in one shape dom
                this.currentVirtualDom_ = null;

                // Cache the created dom
                this.shapeVDomList_ = [];
                this.textVDomList_ = [];
                this.imageVDomList_ = [];

                this.nShapeVEl_ = 0;
                this.nTextVEl_ = 0;
                this.nImageVEl_ = 0;

                // Canvas context properties
                this.strokeStyle = '#000';
                this.fillStyle = '#000';

                this.lineWidth = 1;
                this.lineJoin = 'miter';
                this.lineCap = 'butt';
                this.miterLimit = Z * 1;
                this.globalAlpha = 1;
                // this.font = '10px sans-serif';
                this.font = '12px 微软雅黑';        // 决定还是改这吧，影响代价最小
                this.textAlign = 'left';
                this.textBaseline = 'alphabetic';
                this.canvas = canvasElement;

                var cssText = 'width:' + canvasElement.clientWidth + 'px;height:' +
                    canvasElement.clientHeight + 'px;overflow:hidden;position:absolute';
                var el = canvasElement.ownerDocument.createElement('div');
                el.style.cssText = cssText;
                canvasElement.appendChild(el);

                var overlayEl = el.cloneNode(false);
                // Use a non transparent background.
                overlayEl.style.backgroundColor = '#fff'; //red, I don't know why, it work!
                overlayEl.style.filter = 'alpha(opacity=0)';
                canvasElement.appendChild(overlayEl);

                this.element_ = el;
                this.scaleX_ = 1;
                this.scaleY_ = 1;
                this.lineScale_ = 1;

                this.ghost_ = document.createElement('div');
                var cssText = 'position:absolute; left:0px; right: 0px; top: 0px; bottom: 0px;';
                this.ghost_.style.cssText = cssText;

                this.element_.appendChild(this.ghost_);

                this.x_ = 0;
                this.y_ = 0;
            }

            var contextPrototype = CanvasRenderingContext2D_.prototype;
            contextPrototype.clearRect = function () {
                if (this.textMeasureEl_) {
                    this.textMeasureEl_.removeNode(true);
                    this.textMeasureEl_ = null;
                }
                // var ghost_ = this.ghost_;
                // Hide everything
                this.ghost_.style.display = 'none';
                // NOTES: Using innerHTML = '' will cause all descendant elements detached
                // while (ghost_.firstChild) {
                //   ghost_.removeChild(ghost_.firstChild);
                // }
                // NOTES: removeChild in IE8 will not set the parentNode to null
                //
                // TODO Remove ghost element before change the attributes of children each frame is even more slow
                // if (ghost_.parentNode === this.element_) {
                //   this.element_.removeChild(ghost_);
                // }
                this.currentVirtualDom_ = null;

                this.nShapeVEl_ = 0;
                this.nTextVEl_ = 0;
                this.nImageVEl_ = 0;
            };

            contextPrototype.flush = function () {
                for (var i = 0; i < this.nShapeVEl_; i++) {
                    this.shapeVDomList_[i].flush(this);
                }
                // Show everything
                this.ghost_.style.display = 'block';

                for (var i = this.nShapeVEl_, len = this.shapeVDomList_.length; i < len; i++) {
                    this.shapeVDomList_[i].detach();
                }
                for (var i = this.nImageVEl_, len = this.imageVDomList_.length; i < len; i++) {
                    this.imageVDomList_[i].detach();
                }
                for (var i = this.nTextVEl_, len = this.textVDomList_.length; i < len; i++) {
                    this.textVDomList_[i].detach();
                }
                this.shapeVDomList_.length = this.nShapeVEl_;
                this.imageVDomList_.length = this.nImageVEl_;
                this.textVDomList_.length = this.nTextVEl_;

                // this.element_.appendChild(this.ghost_);
            }

            contextPrototype.beginPath = function () {
                // TODO: Branch current matrix so that save/restore has no effect
                //       as per safari docs.
                this.currentPath_ = [];

                this.currentVirtualDom_ = null;
            };

            contextPrototype.moveTo = function (aX, aY) {
                var p = getSkewedCoords(this, aX, aY);
                p.type = 'moveTo';
                this.currentPath_.push(p);
                this.currentX_ = p.x;
                this.currentY_ = p.y;
            };

            contextPrototype.lineTo = function (aX, aY) {
                var p = getSkewedCoords(this, aX, aY);
                p.type = 'lineTo';
                this.currentPath_.push(p);

                this.currentX_ = p.x;
                this.currentY_ = p.y;

                this.currentVirtualDom_ = null;
            };

            contextPrototype.bezierCurveTo = function (aCP1x, aCP1y,
                                                       aCP2x, aCP2y,
                                                       aX, aY) {
                var p = getSkewedCoords(this, aX, aY);
                var cp1 = getSkewedCoords(this, aCP1x, aCP1y);
                var cp2 = getSkewedCoords(this, aCP2x, aCP2y);
                bezierCurveTo(this, cp1, cp2, p);

                this.currentVirtualDom_ = null;
            };

            // Helper function that takes the already fixed cordinates.
            function bezierCurveTo(self, cp1, cp2, p) {
                self.currentPath_.push({
                    type: 'bezierCurveTo',
                    cp1x: cp1.x,
                    cp1y: cp1.y,
                    cp2x: cp2.x,
                    cp2y: cp2.y,
                    x: p.x,
                    y: p.y
                });
                self.currentX_ = p.x;
                self.currentY_ = p.y;

                this.currentVirtualDom_ = null;
            }

            contextPrototype.quadraticCurveTo = function (aCPx, aCPy, aX, aY) {
                // the following is lifted almost directly from
                // http://developer.mozilla.org/en/docs/Canvas_tutorial:Drawing_shapes

                var cp = getSkewedCoords(this, aCPx, aCPy);
                var p = getSkewedCoords(this, aX, aY);

                var cp1 = {
                    x: this.currentX_ + 2.0 / 3.0 * (cp.x - this.currentX_),
                    y: this.currentY_ + 2.0 / 3.0 * (cp.y - this.currentY_)
                };
                var cp2 = {
                    x: cp1.x + (p.x - this.currentX_) / 3.0,
                    y: cp1.y + (p.y - this.currentY_) / 3.0
                };

                bezierCurveTo(this, cp1, cp2, p);

                this.currentVirtualDom_ = null;
            };

            contextPrototype.arc = function (aX, aY, aRadius,
                                             aStartAngle, aEndAngle, aClockwise) {
                aRadius *= Z;
                var arcType = aClockwise ? 'at' : 'wa';

                var xStart = aX + mc(aStartAngle) * aRadius - Z2;
                var yStart = aY + ms(aStartAngle) * aRadius - Z2;

                var xEnd = aX + mc(aEndAngle) * aRadius - Z2;
                var yEnd = aY + ms(aEndAngle) * aRadius - Z2;

                // IE won't render arches drawn counter clockwise if xStart == xEnd.
                if (xStart == xEnd && !aClockwise) {
                    xStart += 0.125; // Offset xStart by 1/80 of a pixel. Use something
                                     // that can be represented in binary
                }

                var p = getSkewedCoords(this, aX, aY);
                var pStart = getSkewedCoords(this, xStart, yStart);
                var pEnd = getSkewedCoords(this, xEnd, yEnd);

                this.currentPath_.push({
                    type: arcType,
                    x: p.x,
                    y: p.y,
                    radius: aRadius,
                    xStart: pStart.x,
                    yStart: pStart.y,
                    xEnd: pEnd.x,
                    yEnd: pEnd.y
                });


                this.currentVirtualDom_ = null;
            };

            contextPrototype.rect = function (aX, aY, aWidth, aHeight) {
                this.moveTo(aX, aY);
                this.lineTo(aX + aWidth, aY);
                this.lineTo(aX + aWidth, aY + aHeight);
                this.lineTo(aX, aY + aHeight);
                this.closePath();

                this.currentVirtualDom_ = null;
            };

            contextPrototype.strokeRect = function (aX, aY, aWidth, aHeight) {
                var oldPath = this.currentPath_;
                this.beginPath();

                this.moveTo(aX, aY);
                this.lineTo(aX + aWidth, aY);
                this.lineTo(aX + aWidth, aY + aHeight);
                this.lineTo(aX, aY + aHeight);
                this.closePath();
                this.stroke();

                this.currentPath_ = oldPath;
            };

            contextPrototype.fillRect = function (aX, aY, aWidth, aHeight) {
                var oldPath = this.currentPath_;
                this.beginPath();

                this.moveTo(aX, aY);
                this.lineTo(aX + aWidth, aY);
                this.lineTo(aX + aWidth, aY + aHeight);
                this.lineTo(aX, aY + aHeight);
                this.closePath();
                this.fill();

                this.currentPath_ = oldPath;
            };

            contextPrototype.createLinearGradient = function (aX0, aY0, aX1, aY1) {
                var gradient = new CanvasGradient_('gradient');
                gradient.x0_ = aX0;
                gradient.y0_ = aY0;
                gradient.x1_ = aX1;
                gradient.y1_ = aY1;
                return gradient;
            };

            contextPrototype.createRadialGradient = function (aX0, aY0, aR0,
                                                              aX1, aY1, aR1) {
                var gradient = new CanvasGradient_('gradientradial');
                gradient.x0_ = aX0;
                gradient.y0_ = aY0;
                gradient.r0_ = aR0;
                gradient.x1_ = aX1;
                gradient.y1_ = aY1;
                gradient.r1_ = aR1;
                return gradient;
            };
            contextPrototype.drawImage = function (image, var_args) {

                var vDom = this.imageVDomList_[this.nImageVEl_];
                if (!vDom) {
                    vDom = new ImageVirtualDom_();
                    this.imageVDomList_[this.nImageVEl_] = vDom;
                }
                this.nImageVEl_++;
                var args = Array.prototype.slice.call(arguments);
                args.unshift(this);
                var el = vDom.getElement.apply(vDom, args);

                vDom.attachTo(this.ghost_);

                this.currentVirtualDom_ = null;
            };

            contextPrototype.stroke = function (aFill) {
                if (this.currentVirtualDom_) {
                    // Simply append fill or stroke dom
                    if (aFill && !this.currentVirtualDom_.isFilled()) {
                        this.currentVirtualDom_.fill(this);
                    } else if (!aFill && !this.currentVirtualDom_.isStroked()) {
                        this.currentVirtualDom_.stroke(this);
                    }

                    return;
                }

                var pathStr = [];

                var min = {x: null, y: null};
                var max = {x: null, y: null};

                for (var i = 0; i < this.currentPath_.length; i++) {
                    var p = this.currentPath_[i];
                    var c;

                    switch (p.type) {
                        case 'moveTo':
                            c = p;
                            pathStr.push(' m ', mr(p.x), ',', mr(p.y));
                            break;
                        case 'lineTo':
                            pathStr.push(' l ', mr(p.x), ',', mr(p.y));
                            break;
                        case 'close':
                            pathStr.push(' x ');
                            p = null;
                            break;
                        case 'bezierCurveTo':
                            pathStr.push(' c ',
                                mr(p.cp1x), ',', mr(p.cp1y), ',',
                                mr(p.cp2x), ',', mr(p.cp2y), ',',
                                mr(p.x), ',', mr(p.y));
                            break;
                        case 'at':
                        case 'wa':
                            pathStr.push(' ', p.type, ' ',
                                mr(p.x - this.scaleX_ * p.radius), ',',
                                mr(p.y - this.scaleY_ * p.radius), ' ',
                                mr(p.x + this.scaleX_ * p.radius), ',',
                                mr(p.y + this.scaleY_ * p.radius), ' ',
                                mr(p.xStart), ',', mr(p.yStart), ' ',
                                mr(p.xEnd), ',', mr(p.yEnd));
                            break;
                    }

                    // TODO: Following is broken for curves due to
                    //       move to proper paths.

                    // Figure out dimensions so we can do gradient fills
                    // properly
                    if (p) {
                        if (min.x == null || p.x < min.x) {
                            min.x = p.x;
                        }
                        if (max.x == null || p.x > max.x) {
                            max.x = p.x;
                        }
                        if (min.y == null || p.y < min.y) {
                            min.y = p.y;
                        }
                        if (max.y == null || p.y > max.y) {
                            max.y = p.y;
                        }
                    }
                }

                pathStr = pathStr.join('');

                var vDom = this.shapeVDomList_[this.nShapeVEl_];
                if (!vDom) {
                    vDom = new ShapeVirtualDom_();
                    this.shapeVDomList_[this.nShapeVEl_] = vDom;
                }
                this.nShapeVEl_++;

                var shapeEl = vDom.getElement(pathStr, this.x_, this.y_);
                aFill ? vDom.fill(this, min, max) : vDom.stroke(this);

                vDom.attachTo(this.ghost_);

                this.currentVirtualDom_ = vDom;

                return shapeEl;
            };

            contextPrototype.fill = function () {
                return this.stroke(true);
            };

            contextPrototype.closePath = function () {
                this.currentPath_.push({type: 'close'});
            };

            function getCoords(ctx, aX, aY) {
                var m = ctx.m_;
                return {
                    x: Z * (aX * m[0][0] + aY * m[1][0] + m[2][0]) - Z2,
                    y: Z * (aX * m[0][1] + aY * m[1][1] + m[2][1]) - Z2
                };
            };

            function getSkewedCoords(ctx, aX, aY) {
                var m = ctx.m_;
                return {
                    x: Z * (aX * m[0][0] + aY * m[1][0]) - Z2,
                    y: Z * (aX * m[0][1] + aY * m[1][1]) - Z2
                };
            }

            contextPrototype.save = function () {
                var o = {};
                copyState(this, o);
                this.aStack_.push(o);
                this.mStack_.push(this.m_);
                this.m_ = matrixMultiply(createMatrixIdentity(), this.m_);
            };

            contextPrototype.restore = function () {
                if (this.aStack_.length) {
                    copyState(this.aStack_.pop(), this);
                    this.m_ = this.mStack_.pop();
                }
            };

            function matrixIsFinite(m) {
                return isFinite(m[0][0]) && isFinite(m[0][1]) &&
                    isFinite(m[1][0]) && isFinite(m[1][1]) &&
                    isFinite(m[2][0]) && isFinite(m[2][1]);
            }

            function setM(ctx, m, updateLineScale) {
                if (!matrixIsFinite(m)) {
                    return;
                }
                ctx.m_ = m;

                ctx.scaleX_ = Math.sqrt(m[0][0] * m[0][0] + m[0][1] * m[0][1]);
                ctx.scaleY_ = Math.sqrt(m[1][0] * m[1][0] + m[1][1] * m[1][1]);
                ctx.x_ = m[2][0];
                ctx.y_ = m[2][1];

                if (updateLineScale) {
                    // Get the line scale.
                    // Determinant of this.m_ means how much the area is enlarged by the
                    // transformation. So its square root can be used as a scale factor
                    // for width.
                    var det = m[0][0] * m[1][1] - m[0][1] * m[1][0];
                    ctx.lineScale_ = sqrt(abs(det));
                }
            }


            contextPrototype.translate = function (aX, aY) {
                var m1 = [
                    [1, 0, 0],
                    [0, 1, 0],
                    [aX, aY, 1]
                ];

                setM(this, matrixMultiply(m1, this.m_), false);
            };

            contextPrototype.rotate = function (aRot) {
                var c = mc(aRot);
                var s = ms(aRot);

                var m1 = [
                    [c, s, 0],
                    [-s, c, 0],
                    [0, 0, 1]
                ];

                setM(this, matrixMultiply(m1, this.m_), false);
            };

            contextPrototype.scale = function (aX, aY) {
                var m1 = [
                    [aX, 0, 0],
                    [0, aY, 0],
                    [0, 0, 1]
                ];

                setM(this, matrixMultiply(m1, this.m_), true);
            };

            contextPrototype.transform = function (m11, m12, m21, m22, dx, dy) {
                var m1 = [
                    [m11, m12, 0],
                    [m21, m22, 0],
                    [dx, dy, 1]
                ];

                setM(this, matrixMultiply(m1, this.m_), true);

            };

            contextPrototype.setTransform = function (m11, m12, m21, m22, dx, dy) {

                var m = [
                    [m11, m12, 0],
                    [m21, m22, 0],
                    [dx, dy, 1]
                ];

                setM(this, m, true);
            };

            /**
             * The text drawing function.
             * The maxWidth argument isn't taken in account, since no browser supports
             * it yet.
             */
            contextPrototype.drawText_ = function (text, x, y, maxWidth, stroke) {

                var vDom = this.textVDomList_[this.nTextVEl_];
                if (!vDom) {
                    vDom = new TextVirtualDom_();
                    this.textVDomList_[this.nTextVEl_] = vDom;
                }
                this.nTextVEl_++;

                var el = vDom.getElement(this, text, x, y, maxWidth, stroke);

                vDom.attachTo(this.ghost_);

                this.currentVirtualDom_ = null;
            };

            contextPrototype.fillText = function (text, x, y, maxWidth) {
                this.drawText_(text, x, y, maxWidth, false);
            };

            contextPrototype.strokeText = function (text, x, y, maxWidth) {
                this.drawText_(text, x, y, maxWidth, true);
            };

            contextPrototype.measureText = function (text) {
                if (!this.textMeasureEl_) {
                    var s = '<span style="position:absolute;' +
                        'top:-20000px;left:0;padding:0;margin:0;border:none;' +
                        'white-space:pre;"></span>';
                    this.element_.insertAdjacentHTML('beforeEnd', s);
                    this.textMeasureEl_ = this.element_.lastChild;
                }
                var doc = this.element_.ownerDocument;
                this.textMeasureEl_.innerHTML = '';
                this.textMeasureEl_.style.font = this.font;
                // Don't use innerHTML or innerText because they allow markup/whitespace.
                this.textMeasureEl_.appendChild(doc.createTextNode(text));
                return {width: this.textMeasureEl_.offsetWidth};
            };

            /******** STUBS ********/
            contextPrototype.clip = function () {
                // TODO: Implement
            };

            contextPrototype.arcTo = function () {
                // TODO: Implement
            };

            contextPrototype.createPattern = function (image, repetition) {
                return new CanvasPattern_(image, repetition);
            };

            // Gradient / Pattern Stubs
            function CanvasGradient_(aType) {
                this.type_ = aType;
                this.x0_ = 0;
                this.y0_ = 0;
                this.r0_ = 0;
                this.x1_ = 0;
                this.y1_ = 0;
                this.r1_ = 0;
                this.colors_ = [];
            }

            CanvasGradient_.prototype.addColorStop = function (aOffset, aColor) {
                aColor = processStyle(aColor);
                this.colors_.push({
                    offset: aOffset,
                    color: aColor.color,
                    alpha: aColor.alpha
                });
            };

            function CanvasPattern_(image, repetition) {
                assertImageIsValid(image);
                switch (repetition) {
                    case 'repeat':
                    case null:
                    case '':
                        this.repetition_ = 'repeat';
                        break
                    case 'repeat-x':
                    case 'repeat-y':
                    case 'no-repeat':
                        this.repetition_ = repetition;
                        break;
                    default:
                        throwException('SYNTAX_ERR');
                }

                this.src_ = image.src;
                this.width_ = image.width;
                this.height_ = image.height;
            }

            function throwException(s) {
                throw new DOMException_(s);
            }

            function assertImageIsValid(img) {
                if (!img || img.nodeType != 1 || img.tagName != 'IMG') {
                    throwException('TYPE_MISMATCH_ERR');
                }
                if (img.readyState != 'complete') {
                    throwException('INVALID_STATE_ERR');
                }
            }

            function DOMException_(s) {
                this.code = this[s];
                this.message = s + ': DOM Exception ' + this.code;
            }

            var p = DOMException_.prototype = new Error;
            p.INDEX_SIZE_ERR = 1;
            p.DOMSTRING_SIZE_ERR = 2;
            p.HIERARCHY_REQUEST_ERR = 3;
            p.WRONG_DOCUMENT_ERR = 4;
            p.INVALID_CHARACTER_ERR = 5;
            p.NO_DATA_ALLOWED_ERR = 6;
            p.NO_MODIFICATION_ALLOWED_ERR = 7;
            p.NOT_FOUND_ERR = 8;
            p.NOT_SUPPORTED_ERR = 9;
            p.INUSE_ATTRIBUTE_ERR = 10;
            p.INVALID_STATE_ERR = 11;
            p.SYNTAX_ERR = 12;
            p.INVALID_MODIFICATION_ERR = 13;
            p.NAMESPACE_ERR = 14;
            p.INVALID_ACCESS_ERR = 15;
            p.VALIDATION_ERR = 16;
            p.TYPE_MISMATCH_ERR = 17;

            // set up externs
            G_vmlCanvasManager = G_vmlCanvasManager_;
            CanvasRenderingContext2D = CanvasRenderingContext2D_;
            CanvasGradient = CanvasGradient_;
            CanvasPattern = CanvasPattern_;
            DOMException = DOMException_;
        })();

    } // if
    else { // make the canvas test simple by kener.linfeng@gmail.com
        G_vmlCanvasManager = void 0;
    }
    return G_vmlCanvasManager;
}); // define